Greenwood Michael S., Cui Xiuyu, Xu Fuyu
Department of Forest Ecosystem Science, 5755 Nutting Hall, University of Maine, Orono, ME 04469-5755, USA; 1315 Morrene Road, Apartment 17f, Durham NC 27705, USA.
Physiol Plant. 2001 Mar;111(3):373-380. doi: 10.1034/j.1399-3054.2001.1110315.x.
Hypocotyl cuttings (from 20- and 50-day-old Pinus taeda L. seedlings) rooted readily within 30 days in response to exogenous auxin, while epicotyl cuttings (from 50-day-old seedlings) rarely formed roots within 60 days. Responses to auxin during adventitious rooting included the induction of cell reorganization and cell division, followed by the organization of the root meristem. Explants from the bases of both epicotyl and hypocotyl cuttings readily formed callus tissue in response to a variety of auxins, but did not organize root meristems. Auxin-induced cell division was observed in the cambial region within 4 days, and later spread to the outer cortex at the same rate in both tissues. Cells at locations that would normally form roots in foliated hypocotyl cuttings did not produce callus any differently than those in other parts of the cortex. Therefore, auxin-induced root meristem organization appeared to occur independently of auxin-induced cell reorganization/division. The observation that N-(1-naphthyl)phthalamic acid (NPA) promoted cellular reorganization and callus formation but delayed rooting implies the existence of an auxin signal transduction pathway that is specific to root meristem organization. Attempts to induce root formation in callus or explants without foliage were unsuccessful. Both the cotyledon and epicotyl foliage provided a light-dependent product other than auxin that promoted root meristem formation in hypocotyl cuttings.
下胚轴插条（取自20日龄和50日龄的火炬松幼苗）在30天内对外源生长素反应迅速生根，而上胚轴插条（取自50日龄幼苗）在60天内很少生根。不定根形成过程中对生长素的反应包括诱导细胞重组和细胞分裂，随后形成根分生组织。上胚轴和下胚轴插条基部的外植体对多种生长素反应均易形成愈伤组织，但未形成根分生组织。生长素诱导的细胞分裂在4天内在形成层区域观察到，随后在两种组织中以相同速率扩散到外皮层。在有叶下胚轴插条中通常会形成根的位置的细胞产生愈伤组织的方式与皮层其他部位的细胞没有任何不同。因此，生长素诱导的根分生组织形成似乎独立于生长素诱导的细胞重组/分裂。N-（1-萘基）邻苯二甲酸（NPA）促进细胞重组和愈伤组织形成但延迟生根这一观察结果表明存在一条特定于根分生组织形成的生长素信号转导途径。在无叶的愈伤组织或外植体中诱导生根的尝试未成功。子叶和上胚轴叶片都提供了一种除生长素外的光依赖产物，该产物促进下胚轴插条中根分生组织的形成。
